Custom car seat covers are actually dangerous - they aren't crash tested, aren't fire resistant, and ALL car seat manufacturers forbid their use. They void your carseat warranty - meaning that, if you crash, your insurance isn't going to cover the seat OR the injuries caused in it. Don't risk it. Use the legal, manufacturer-approved cover that came with your seat.
The KeyFit 30 Zip Infant Car Seat from Chicco offers superior safety and comfort features plus the added functional convenience of a zip-off canopy, zip-on visor, and zip-around boot. Comes with a machine-washable, quick-remove seat pad for easy cleaning.